Jacob Stephens,
Will Heffern
Gordon
College
Department
of Biology
255
Grapevine Road, Wenham Massachusetts, 01984; [email]
Experimental
1.
Chemicals and materials
Copper wire and sand paper were purchased from Home Depot (Danvers, MA). Nitric acid (HNO3) (conc.), sulfuric acid (H2SO4), 3.0 M sodium hydroxide (NaOH), and evaporating dishes were obtained from Fisher Scientific (Pittsburgh, PA). The boiling chips were obtained from Acros Organics (Geel, Belgium). Zinc powder was obtained from Alfa-Aesar (Ward Hill, MA). Acetone was obtained from Pharmco (Brookfield, CT). 18 MΩ Millipore grade deionized water was used.
2.
Copper redox reaction with nitric acid to form copper nitrate, water,
and nitrogen dioxide
Cu(s) +
4HNO3(aq) Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)
Sandpaper
was used to clean an approximately 0.500 g strip of #16 copper wire. Then the
mass of the wire was measured to the nearest 0.0001 g with a digital scale and
recorded. The wire was then placed into a 250 mL beaker. The beaker was then
placed under the hood to have two plastic-pipets-full (about 5 mL total) of
concentrated nitric acid (HNO3) added. The copper immediately began
to react with the nitric acid and was kept under the hood until the reaction completed.
Then beaker was transferred to the laboratory bench and had 100 mL of deionized
water added.
3.
Copper nitrate double replacement reaction with sodium hydroxide to form
copper hydroxide and sodium nitrate
Cu(NO3)2(aq)
+ 2NaOH(aq) Cu(OH)2(s) + 2NaNO3(aq)
Next, 30
mL of 3 M sodium hydroxide (NaOH) was added to the solution in the beaker.
4.
Copper hydroxide decomposed by heat to form copper and water
Cu(OH)2(s) CuO(s) + H2O(l)
Two
boiling chips (three would have worked as well) were then added to the
solution. The solution was then carefully heated until it just began to boil
while being stirred with a stirring rod.
5.
Copper oxide double replacement reaction with sulfuric acid to form
copper sulphate and water
CuO(s) + H2SO4(aq)
CuSO4(aq) + H2O(l)
The black
solid formed by the previous reaction was allowed to settle, and then the
supernatant liquid was decanted. 200 mL of nearly boiling deionized water was
then added. The solution was stirred, and then the solid was again allowed to
settle. The solution was decanted again. Next 15 mL of 6 M sulfuric acid
(H2SO4
(aq)) was added.
6.
Copper sulphate and sulfuric acid single replacement reaction
with zinc to form zinc sulphate, copper, and dihydrogen
CuSO4(aq)
+ Zn(s) ZnSO4(aq)
+ Cu(s)
The
boiling chips were removed with tweezers, and then the beaker was taken back to
the hood. 2.0 g of 40-mesh zinc metal (Zn(s)) was added. A redox reaction
between the Zn(s) and excess H2SO4 took place in the
beaker after the Zn(s) was added.
7.
Isolation of copper
After the
zinc dissolved and the supernatant liquid became clear, two drops of
concentrated ammonia were added to test for Cu2+(aq), and a blue complex was
formed. The solution was then heated gently to ensure that the zinc was
completely dissolved, the the solution was allowed to
cool.
As the solution was cooling, a porcelain
evaporating dish was weighed. When the solution cooled and precipitated copper
settled to the bottom of the beaker, the supernatant was decanted
and the copper transferred to the porcelain evaporating dish. The precipitate
was washed with 5 mL deionized water, allowed to settle, and then the liquid
decanted. The washing process was repeated. Acetone was used as the final
washing solution.
After the second washing, the copper sample
was dried. When the copper sample dried, the copper was discarded into the hood.